Metric Compression Ratio Calculator
Every input in millimeters and cubic centimeters. Every output in bar and kPa. Built for European and Japanese engine builders who work in the metric system by default.
Dynamic Compression (Slider-Crank)
Metric ↔ Imperial Conversions Every Engine Builder Needs
Cross-referencing a German service manual with a US piston catalog? This table covers the conversions you'll do most often without reaching for your phone.
Popular Metric Engine Specs
European and Japanese engines you'll encounter on this calculator — click any preset above to auto-fill all values.
| Engine | Origin | Bore (mm) | Stroke (mm) | Chamber (cc) | Stock CR |
|---|---|---|---|---|---|
| BMW M50B25 | Germany | 84 | 75 | 44 | 10.5:1 |
| Jaguar AJ6 (3.2L) | UK | 91 | 83 | 45 | 9.5:1 |
| VW 2.0TFSI EA888 | Germany | 82.5 | 92.8 | 45 | 10.5:1 |
| Opel 2.0L Turbo | Germany | 86 | 86 | 40 | 10.5:1 |
| Volvo B5244T5 | Sweden | 83 | 90 | 48 | 8.5:1 |
| Renault F4Rt 2.0T | France | 82.7 | 93 | 42 | 9.0:1 |
| BMW S54 (E46 M3) | Germany | 87 | 91 | 35 | 11.5:1 |
| Nissan RB26DETT | Japan | 86 | 73.7 | 51 | 8.5:1 |
| Honda F22C (S2000) | Japan | 87 | 90.7 | 44 | 11.1:1 |
| Mazda 13B-MSP Renesis | Japan | 80 | 60 | 65 | 10.0:1 |
Metric CR Calculator FAQs
Can I mix metric and imperial inputs?+
Yes — the main engine-calculator component handles mixed units natively. This page is a dedicated 'all-metric' mode for European and Japanese builds where everything is specified in mm/cc/bar. If you have a US piston catalog and a German head spec sheet, either mode works fine.
Why bar and kPa instead of PSI?+
Most of the world measures cylinder pressure in bar (1 bar ≈ 14.5 PSI) or kilopascals (100 kPa = 1 bar). A metric compression gauge reads directly in bar, so you don't need to mentally convert from PSI. 10 bar is roughly 145 PSI.
How accurate is the mm→inch conversion?+
Internationally defined: 1 inch = exactly 25.4 mm. 1 cc = 16.387064 cubic inches. Our calculator uses these exact values, so mixed-unit calculations are mathematically identical whether you input mm or inches.
More Compression Calculators
Every tool in the Engine Calculator family shares the same compression math — metric or imperial, always consistent.